Laid a membrame with small stone chippings over the top , NOW weeds are coming through...

Before you moan about it, are the roots above or below the membrane? If they are above then the seeds have blown in. Either way, I would just mix some Weedol in a sprayer and kill the weeds off. Alternatively, sodium chlorate solution watered in will prevent all growth for about six months.

Hi Diy , thank you for your fast reply , okay but if there below , should the membrame not stop this happening , it was only laid 8 months ago? how would i know if they are from above or below ? if from below i guess they have come through the membrame , but if from above i guess they have gone through the membrame also ?

If the stone chippings are lose I would dig down with a hand trowel and see if the roots are above or below the membrane. As far as I know the membrane should let rain water drain through but shouldn't let plants grow through. Excluding light and air normally kills most weeds in my experience.

Bird droppings containing seeds. The dropping provides enough nutrient for the seed to grow

How deep is the chipping layer? How big is the overlap on the fabric?

As others have said the weeds are probably growing in the gravel but it isn't impossible for the roots to grow down through the membrane into the soil below. I've found that happen especially witha cheap membrane.